Some teleconferencing systems use a plurality of microphone units or clusters distributed over a room. The audio reception quality of the microphone units may be monitored in order to select the microphone units or clusters that receive the source signal with the best quality. The system may use the output from a selected microphone unit or cluster, or may mix the outputs of several selected microphone units or clusters and use it as the system output.
There are various selection methods that use different parameters such as the received signal strength and the signal to noise ratio (SNR) and different algorithms for determining which microphone unit has the best quality. Since the level of reverberation may significantly affect the intelligibility of speech, some selection methods try to estimate the level of reverberation received by a microphone unit and to use it as parameter for selection. In some known methods, the level of reverberation is estimated according to the signal power or the SNR, for example based on the assumptions that the level of noise is uniform, the level of reverberation is uniform across the room and that all the microphone units have the same sensitivity, i.e., the same proportion between the acoustic pressure on the microphone unit and its output signal. Based on these assumptions, for example, the signal with the maximal received power may be considered as the least reverberant signal. However, this is not always the case, and often some areas in the room are significantly more reverberant than other areas, and the sensitivity of the microphone units often varies from unit to unit.
Some more sophisticated known methods for estimating the reverberation levels usually are not suitable for real-time monitoring or are not suitable for speech signals, and therefore may not be suitable for teleconferencing systems. For example, some of these methods require signal segments that are too long for real-time monitoring or require a normalized and/or spectrally white source signal. Some other methods use complicated and expensive devices and analyses that may be suitable for a unique measurement for evaluating the directional distribution of arriving energy and the degree and diffuseness of sound fields in a given room, but that may not be suitable for a constantly changing environment and audio sources and/or for dynamic real time reverberation measurements.